Coatings are applied to various surfaces to protect the surface. For example, coatings are used to waterproof and insulate and to prevent corrosion, rust, rot, water damage, fouling, burning, as well as other types of deterioration and damage to a surface. The surfaces may include, but are not limited to, metal, wood, concrete or a synthetic, such as composites, tile, foam, fiberglass, PVC, plastic or the like, as for example. The surface may be the surface of a vehicle, piping, tubing, a vessel, furniture, caskets, structures (such as flooring, roofing, decking, etc.) to name a few. It is important that the coatings are effective, are inexpensive to apply and maintain, and have an extended lifetime.
In one application of coatings, surfaces exposed to sea wash or water containing marine organisms are susceptible to fouling. For example, the hull of a ship is designed to cut through the water with minimal resistance for maximum efficiency of the wind or mechanical power driving the vessel. In addition to a hydrodynamics design, the hull should be clean and smooth. However, with time (often relatively quickly), the hulls of ships or other exposed surfaces become fouled by all types of organic and inorganic material, i.e., the attachment of organisms to the exposed surfaces. Other structures exposed to water may also become fouled. Barnacles, bryozoans, mollusks, mussels, annelids, tunicates, algae, slimes and hydroids make up the most common type of fouling marine organisms.
The consequences are significant. Fouling causes the once smooth hull to become extremely rough, promoting corrosion, weakening the hull, eventually decreasing the ships maneuverability and increasing drag. The domino effect is obvious—fuel consumption is increased (in some cases by as much as 30%), which causes both economic (e.g., increased fuel costs) and environmental consequences (e.g., increased greenhouse gases). Not surprisingly, a significant amount of attention has been devoted to this problem.
Historically, one solution was to frequently scrape or blast the hull clean to remove the fouling. However, this cumbersome process is time consuming and costly. In addition, frequent scraping of the hull can result in weakening the hull. The most widely accepted method of controlling and/or preventing fouling is to apply some type of anti-fouling coating on the surfaces. Common anti-fouling coatings contain amounts of metals, e.g., copper, aluminum or tin, which the organisms find distasteful, even toxic. As an added benefit, the coatings also prevent corrosion.
Anti-fouling compositions have been known for years. Although such anti-fouling compositions are an improvement, they do not represent a perfect solution. Several problems exist today, e.g., applying the coating evenly, difficulty in handling the material, the need for an efficient, consistent and durable apparatus for applying the materials, and the fact that the coatings are notorious for their inability to adhere to the surfaces. For example, U.S. Pat. No. 2,602,752 discloses an anti-fouling composition designed by the U.S. Navy to prevent the fouling of the hulls of vessels. In fact, the composition developed in U.S. Pat. No. 2,602,752 achieved minimal success because of the difficulty of the coating adhering to the metal ship hulls and because of the difficulty in achieving an even, smooth, homogenous coating. This is in part due to the high solids content. The material described in U.S. Pat. No. 2,602,752 has essentially a solids content of essentially 100%. Paint typically has a solids content of about 50-60% and other anti-fouling compositions have a solids content of about 60-75%.
In addition, the anti-fouling chemicals and spray technology required high handling temperatures, e.g., greater than or equal to about 300° F., to reduce viscosity and keep the material fluid. These high temperatures create difficult equipment and handling requirements. New problems have also emerged.
The anti-fouling coatings on the market today leach toxic metal compounds into the water. The high leaching of toxic metal compounds over short periods of time unnecessarily contaminates the water. Regulatory agencies are seeking to limit the amount of leaching that can take place over a specified period of time, e.g., for the metal copper, regulations in Sweden require less that 55 μg/cm2/day, Canada requires less than 40 μg/cm2/day. In addition, high leaching results in a shorter lifetime of the coating, i.e., once the toxic chemicals have been leached away, the coating will no longer be a deterrent to fouling organisms. Accordingly, coatings with a slower but effective leach rate can provide the added benefit of longer and extended lifetimes.
Further, the lifetime of coatings on the market today is relatively short in that ships have to be dry docked for cleaning at a frequency of about every 18 months. The process currently utilized for applying anti-fouling coatings requires having the ship in dry dock for weeks. Generally, the process involves about one day to blast the hull clean, at least one day to prime the hull, several days for the primer to completely dry, followed by a minimum of two weeks to coat the hull with the anti-fouling paint. Five to six coats are necessary and each coat involves about one day for application and about two days for drying. Every day represents a significant loss for the ship owner in that they are paying to be in dry dock and losing money due to the ship being out of commission.
In addition, the organic compounds present in the prior art anti-fouling coatings pose a pollution problem and they require volatile organic compounds (VOC) to assist in application and drying.
At present, two significant areas of interest with respect to using anti-fouling coatings remain i.e., how to achieve a better bond between the coating and the metal surface and more efficient and productive means for applying the coatings, particularly at higher temperatures. Accordingly, improvements need to be made in the field. The present invention addresses the deficiencies of the prior art discussed above.